This invention relates to a system for fixing co-rotating axial flow blades with twist and staged so that both wake interceptions for a variety of relative velocities and, adjacent equidistant blade spacing are realized so as to provide acoustic and/or efficiency benefit.
Given that blades with twist, tending to uniform advance in axial flow, normally produce swirling wake sheets, one for each blade. And given that each propagation generally represents swirling energy loss and a source of noise radiation. And given that co-rotating discs of blades with roots fixed to a common axis of rotation and with uniformly advancing swirling wakes of upstream blades that are substantially capable, when staged, of intercepting or interacting with downstream blades.
While such interactions are generally thought to be detrimental, if all other things are equal, it seems desirable to reduce net wake production. By equidistantly spacing separate blades in adjacent stages coincident with effective near wake interception the invention realizes a complex of beneficial wake interactions hitherto unsuspected. Virtual wake reduction here realizes an acoustic benefit. Many acoustic reduction systems incurring general efficiency losses are known, and despite the general belief that wake interactions are detrimental, it is a feature of this invention that increased efficiency is realized whereby some of the energy of the swirling wakes is harnessed to beneficially work upon the following blades under a range of some practical conditions.
That is, by critically locating uniformly advancing co-rotating staged blades to realize the synergizing complex of interactions described herein, the sum of the blades can practically be made to produce less noise and/or to often act more energy efficiently than conventional single disc embodiments, or than any of the factors taken separately. In this specification and claims, synergy means that the combination of factors realizes benefits greater than any of the factors acting separately.
Historically, work by Eiffel Tietjens Prandtl and others has led erroneously to a general belief in the in efficiency of staged foils due to interactions thought detrimental. Nonetheless some others have noted special relative advantage of some co-rotating stage systems. Ward, U.S. Pat. No. 3,625,631 teaches avoidance of coplanar non-uniform blade wake interactions by variable geometry staging. Shipes, U.S. Pat. Nos. 3,768,546 and Rosen, 2,982,361 teach compact co-operation with devices that teach a substantial and essential zero net axial space between at least the first two discs of adjacent co-rating blade stages fixed to a common axis of rotation such that the rear element of the upstream blades substantially describe a disc common or adjacent to that described by the front element of the downstream blades.
That is to attain compact interactions these embodiments deliberately avoid planform symmetry/equidistant blade spacing yet such symmetry/equidistance, sacrificing maximum compactness, is the fixed variable required by the present invention to synergize blade phase absorption in the presence of near wake interception.
Rosen claims acute index advance angles specifically denying symmetrical planforms. Shipes et al index advance claims teach some interaction avoidance so as to fix angles, to show assymetrical, or more extreme alternate zero blade separation, planforms. The effective function of both these planform assymetries is to substantially approach or realize first stage blade frequency reinforcement, whereas the symmetrical/equidistant staged interacting planform can substantially approach first stage frequency reduction or cancellation.
I thus conclude that hitherto known co-rotating staged uniform wake-producing systems do not know, claim or have the capacity to realize specific performance superior to known conventional single stage configurations for axial flow fans and propellors, while non-uniform wake producing variably staged systems taught wake avoidance and deliberately and substantially lacked capacity for wake interception.
Thus no prior staged system has realized the complex or synergizing relations herein disclosed.